This invention relates generally to controls used in liquid transfer systems, and more particularly, to an overflow prevention mechanism which prevents overflow of a container such as a fuel tank when a liquid such as fuel is being transferred thereto, particularly in systems where such transfers occur on a repeating basis.
In some internal combustion engine applications, particularly large engines used in generator applications, it is desirable to assure that the engine has a relatively continuous supply of fuel available. If fuel delivery to the engine is interrupted the engine will quit running and power output from the generator will likewise cease, causing an undesired blackout in those situations where the generator is relied upon for power.
Large engines in generator applications are typically provided with a small fuel tank which might hold enough fuel to run the engine for about a day. The fuel tank is connected to a larger, bulk fuel tank or other main source of fuel which can be used to fill the fuel tank as needed. For example, a pump may be connected between the main source of fuel and the fuel tank. The fuel tank may include a low fuel level sensor and a high fuel level sensor, both connected through a controller to control a normally-open motor relay, which motor relay is connected between a source of electrical energy and a motor which operates the pump. The low fuel level sensor acts as a pump start sensor in that if the level of fuel in the fuel tank falls to the low level, the low fuel level sensor produces an output which is provided to the controller and the controller responsively energizes the motor relay to connect the motor in circuit with the electrical energy source. Fuel is transferred from the main source of fuel to the fuel tank during operation of the pump. The high fuel level sensor acts as a pump stop sensor in that when the level of fuel in the fuel tank reaches the high level, the high fuel level sensor produces an output which is provided to the controller and the controller responsively de-energizes the motor relay causing the motor to stop and likewise causing the transfer of fuel to stop.
A potential problem with such fuel transfer systems is that if the current supplied through the relay is too high, arcing may occur and cause the motor relay to essentially weld itself in the closed position. In such cases, even where the failed motor relay is de-energized, the motor relay may remain closed causing fuel transfer to the fuel tank to continue past the desired stopping point unless the pump motor is manually turned off. Such situations can result in undesired overflow of the fuel tank.
Other types of liquid transfer systems include normally-open switching devices which may be subject to failing in a closed position due to arcing which results from repeated closing and opening of such devices. The mere addition of another normally-open switching device such as a relay in such circuits cannot satisfactorily address the problem because, for example, if one normally-open motor relay fails in the closed position due to arcing it is possible that another similar normally-open motor relay will also fail in the closed position due to arcing.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a liquid transfer system for repeatedly transferring a liquid from a main liquid source to a container while preventing overflow of the container is provided. A liquid path connects the main liquid source to the container. An electrically controllable flow control device is positioned along the liquid path for enabling controlled delivery of liquid from the main liquid source to the container along the liquid path. A liquid level sensor is provided for sensing when the level of liquid within the container rises to a predetermined extreme high level. A normally-closed switching device is connected between a source of electrical energy and the electrically controllable flow control device. The liquid level sensor is operatively connected to the normally-closed switching device for effecting the opening thereof when the level of liquid in the container reaches the predetermined extreme high level such that further liquid transfer to the container is prevented.
In another aspect of the present invention an overflow prevention mechanism for use in association with a fuel transfer system is provided, where the fuel transfer system includes a pump connected between a source of fuel and a fuel tank which may be filled with fuel from the source of fuel by operation of the pump, a relay connected between a source of electrical energy and a pump motor which operates the pump, and a fuel level sensor for sensing when the fuel level within the fuel tank reaches a predetermined high level at which it is desired to stop further fuel transfer thereto, the fuel level sensor operatively connected to the relay to effect control thereof. The overflow prevention mechanism includes a backup fuel level sensor and a shunt trip breaker. The backup fuel level sensor senses if the level of fuel within the fuel tank reaches an extreme high level which is higher than the predetermined high level. When the fuel level within the tank reaches the extreme high level the backup fuel level sensor produces an output indicative of the fuel having reached such extreme high level. The shunt trip breaker is connected between the source of electrical energy and the pump motor in circuit with the relay when such relay is closed. The shunt trip breaker is operatively connected to the backup fuel level sensor so as to respond to the production of the backup fuel level sensor output by opening, thereby disconnecting the pump motor from the electrical energy source when the fuel level within the fuel tank reaches the extreme high level.